To test whether a set of samples can be well modeled as white
noise, we may compute its sample autocorrelation and verify
that it approaches an impulse in the limit as the number of
samples becomes large; this is another way of saying that successive
noise samples are uncorrelated. Equivalently, we may break the
set of samples into successive blocks across time, take an FFT of
each block, and average their squared magnitudes; if the resulting
average magnitude spectrum is flat, then the set of samples
looks like white noise. In the following sections, we will describe
these steps in further detail, culminating in Welch's method
for noise spectrum analysis, summarized in §6.9.